This invention relates to a flexible coupling that effectively accommodates shaft misalignments, absorbs shock and damps vibration using coil springs as the flexible member in the torque transmitting mechanism.
One type of flexible shaft coupling uses coil springs as its flexible member. In one variation of this type, the coil springs are disposed to change their shape in a direction perpendicular to the axis thereof. This type of flexible shaft coupling comprises a first and a second hub each having a flange at one end thereof and adapted for connection of the transmission shaft, a cover fastened to the flange of the second hub in such a manner as to allow passing therethrough of a cylindrical part of the first hub and accommodate the flange of the first hub, and coil springs passing through each of multiple spring holes provided along the periphery of the flange of the first hub. The first and second hubs are disposed so that the flanges thereof face each other with a clearance gap and the coil springs are compressed between the flange of the second hub and the cover. Torque is transmitted between the first and second hubs via the coil springs. Japanese Provisional Patent Publication S59-212528 (U.S. Pat. No. 4,639,237) discloses this type of flexible shaft coupling.
Requiring no spring seat, flexible shaft couplings of this type have advantages such as a simple and small structure and a small moment of inertia. However, the coil springs, which resist the load at each center portion of their springs perpendicularly to each spring axis, therefore receive great stress and are not allowed to deflect greatly. When the coupling is installed in some equipment, the permissible allowance of shaft misalignments, driving torque, absorbing shocks and reducing vibration is comparatively smaller than required.
To eliminate the smaller allowance of shaft misalignments, driving torque and reducing vibration, the inventor invented the flexible shaft coupling described below. The coil springs are barrel-shaped coil springs whose largest outside diameter portion is closely fit in the spring hole in the first hub and the smallest inside diameter portion is closely fit over the spring supporting pin held between the flange of the second hub and the cover. The barrel-shaped springs are interposed, in a compressed state, between the flange of the second hub and the cover so that, when torque is transmitted, the barrel-shaped coil springs deform and come into contact with adjoining coils thereof. Japanese Provisional Patent Publication H6-213247 (U.S. Pat. No. 5,795,231) discloses this type of flexible shaft coupling.
The barrel-shaped coil springs in the flexible shaft coupling described above increases in outside diameter as transmitted torque increases. This, in turn, results in increased coupling outside diameter and increased moment of inertia.